Taxonomic and metabolic profiling of glacial ice algal communities on the Greenland Ice Sheet

During the summer melt season, glacier ice algal blooms are widespread in the area termed “dark

zone” in the southwest region of Greenland. Due to their pigmentation, glacier ice algae reduce the

albedo of the ice sheet, increasing surface melting. Despite their crucial role in the Greenland Ice Sheet

(GrIS) ecosystem, we know little about their metabolic potential or functions. Here, we present insights

into the links between microbial community composition using 18S and ITS2 sequencing and total

metabolic profiling of samples dominated by glacier ice algae from the GrIS. Our analysis of ITS2

secondary structures reveals that blooms are dominated by a single algal species, yet glacier ice algal

haplotype composition differs between sites (along a 40 km transect) and surface habitats (clean snow

vs. high algal biomass ice). Furthermore, metabolic composition changes during the development of

glacier ice algal blooms with an accumulation of fatty acids, although few differences were observed

between sites along the transect. In addition, a few metabolites showed diurnal variations and our data

suggest that under low light and freezing conditions, chlorophyll degradation, tocopherol abundance

and phytol remobilization may be the key compounds changing in the glacier ice algae dominated

samples. Overall, these results improve our understanding of the chemical environment in the GrIS

supraglacial microbial community structure and the contribution of the primary producers dominated

by the glacier ice algae. Our data also show that endo- and exo-metabolic patterns need to be

differentiated and that multiplexed data sets will help gain a better insight into these complex algae-

controlled ecosystems.